The present invention relates to a speaker for an electronic instrument such as a portable telephone.
In recent years, there is used a thin electrodynamic speaker having an excellent quality for the portable telephone. Dimensions of parts in the speaker, in particular, position accuracy of the voice coil disposed in the magnetic circuit have an influence on sound quality. Therefore, it is necessary to severely check the position accuracy.
A conventional speaker will be described hereinafter with reference to FIGS. 4 and 5.
The speaker comprises a lower frame assembly 51 and an upper frame assembly 52.
The lower frame assembly 51 comprises an annular lower frame 61 made of plastic, a tray shape yoke 62 made of magnetic material and embedded in the lower frame, a permanent magnet 63 secured to the yoke and a top plate 64 made of magnetic material and secured to the permanent magnet 63. A magnetic circuit is formed by the top plate 64, permanent magnet 63 and the yoke 62 to form a magnetic gap 66 between the peripheral wall of the top plate 64 and the inside wall of an upper portion of the yoke 62.
On the upper surface of the lower frame 61, an annular projection 61a is formed at a peripheral portion thereof and an annular step 61b is formed outside the projection 61a. 
The upper frame assembly 52 comprises an annular upper frame 71 made of plastic, a diaphragm 73, a voice coil 74 secured to the underside of the diaphragm 73, and a protector 75 having a plurality of sound discharge openings. A pair of leads 72 are embedded in the upper frame 71 and projected from the upper frame and downwardly bent.
The upper frame 71 has an annular upper step 71a on the upper surface thereof, and an annular lower step 71b. The diaphragm 73 is adhered to the lower step 71b and the protector 75 is adhered to the upper step 71a. 
Both ends 74a of the voice coil 74 are projected from the upper frame 71 passing through holes formed in the frame and connected to the leads 72, respectively.
FIG. 5 shows both the lower and upper frame assemblies 51 and 52.
The upper frame 71 is secured to the step 61b of the lower frame 61 by the ultrasonic welding, so that the voice coil 74 is disposed in the magnetic gap 66.
In order to allow the vibration of one of the frame assemblies in the ultrasonic welding operation, there is provided a clearance B between the inside wall of the upper frame 71 and the outside wall of the projection 61a of the lower frame 61. However, the clearance (0.05-0.1 mm) causes central positions of the lower and upper frames 61 and 71 to deviate from each other when both frame assemblies are coupled with each other. As a result, the position of the voice coil 74 is not accurately positioned in the magnetic gap 66, so that the sound quality of the speaker deteriorates.
An object of the present invention is to provide a speaker in which the voice coil can be accurately positioned in the magnetic gap.
According to the present invention, there is provided a speaker for an electronic instrument comprising a lower frame assembly comprising a lower frame provided with a yoke, a permanent magnet secured to the yoke, and a top plate secured to the permanent magnet, an upper frame assembly comprising an upper frame provided with a diaphragm secured to the upper frame, and a voice coil secured to the diaphragm and disposed in a magnetic gap between the yoke and the top plate, wherein a plurality of grooves are formed in a peripheral wall of the lower frame, a plurality of engaging portions are formed on the upper frame, corresponding to the grooves of the lower frame, each of the engaging portions comprises an engaging plate and a hook formed at an end of the engaging plate.
Each of the engaging portions comprises an elastic engaging plate axially projected from an underside of the upper frame, and a hook formed at an end of the elastic engaging plate so as to be engaged with an underside of the lower frame.
These and other objects and features of the present invention will become more apparent from the following detailed description with reference to the accompanying drawings.